Preparation and enantiomer separation behavior of selectively methylated γ-cyclodextrin-bonded stationary phases for high-performance liquid chromatography

Native and three selectively methylated gamma-cyclodextrin (gamma-CD)-bonded stationary phases without an unreacted spacer arm for HPLC were prepared, where octakis(2-O-methyl)-gamma-CD, octakis(3-O-methyl)-gamma-CD and octakis(2,3-di-O-methyl)-gamma-CD were used as the methylated gamma-CDs. The enantiomer separation abilities of the resulting gamma-CD stationary phases for 11 pairs of dansylamino acid enantiomers as model solutes were investigated. The effects of pH and methanol content of the mobile phase on the retention and resolution were examined to optimize the mobile phase conditions. The optimum resolution was achieved using a mobile phase consisting of 1.0% triethylammonium acetate buffer (pH 5.0)-methanol (8:2, v/v). gamma-CD-bonded stationary phase and octakis(3-O-methyl)-gamma-CD-bonded stationary phase exhibited good enantiomer separation ability for the dansylamino acids among the four gamma-CD stationary phases examined in this study. In particular, octakis(3-O-methyl) -gamma-CP-bonded stationary phase showed the better enantiomer separation than gamma-CD-bonded stationary phase except for dansyl-Dr-leucine and -glutamic acid. Octakis(2-O-methyl)- and octakis(2,3-di-O-methyl)-gamma-CD-bonded stationary phases had no enantiomer separation abilities for those solutes. The results suggest the important role of the hydroxyl groups at the 2-positions on the rim of the gamma-CD cavities in the enantiomer separation for the dansylamino acids. (C) 1999 Published by Elsevier Science B.V. All rights reserved.